1. Field of this Invention
This invention relates to polyvinylchloride products and in particular, lubricants for polyvinyl chloride products.
Polyvinylchloride articles are useful for a number of purposes ranging from highly flexible inductile materials to those which are quite rigid. This invention is particularly concerned with the manufacture of rigid polyvinylchloride articles and particular to a novel lubricant system for rigid polyvinylchloride articles.
It is generally known that polyvinylchloride will adhere to the sides of the equipment in which it is processed. Typically, polyvinylchloride is mixed with other useful ingredients including lubricants and is masticated in an extruder. Twin screw extruders are often used with the pellets of polyvinylchloride being added together with the other ingredients at one end of the extruder. The extruder, by crushing and pushing the polyvinylchloride articles together, forms a liquid melt.
The molten-state polyvinylchloride is then pushed through the extruder and eventually extruded through a die. At any point in the processing where the polyvinylchloride contacts metal the possibility of adhesion occurs. In a free-flowing process the polyvinylchloride moves through the extruder and is easily extruded through the die. However, when the process is interrupted or the flow is stopped in the extruder the possibility occurs for the polyvinylchloride to adhere. Even without the adhesion in the extruder it is possible for the polyvinylchloride to resist flow through contact with the extruder walls.
The contact of the polyvinylchloride with the extruder walls requires greater physical energy to move the polyvinylchloride through the extruder. As the extruder is typically connected to a constant rpm motor the flow of polyvinylchloride should be smooth through the extruder. If the flow of the polyvinylchloride is restricted by adhesion to the walls of the extruder the motor may become overworked. At the very least, greater energy expenditures are observed when lubrication is not properly utilized to continue the flow of the polyvinylchloride through the extruder.
There are attendant difficulties in utilizing polyvinylchloride lubricants. These difficulties involve adverse consequences to the polyvinylchloride articles. The present invention exhibits both internal and external polyvinylchloride lubricating properties. An internal lubricant for polyvinylchloride is one which assists in the movement of the molecules of polyvinylchloride over one another to ensure that an even melt is achieved in the extruder. The adverse consequences which can result from utilizing an improper internal lubricant are primarily concerned with the heat distortion caused by the flexibility of the article which in turn is caused by the lubricant.
External lubricants are those which primarily contact the walls of the extruder and of the die. The purpose of the external lubricant is to facilitate the passage of the polyvinylchloride through the extruder. Ordinarily, the external lubricant is desired to be left on the walls of the extruder or the die and that the external lubricant migrate to the surface of the finished polyvinylchloride article. It is thus possible by correctly choosing an external lubricant to have one which may be cleaned from the finished article so that the article may be painted or otherwise treated.
A lubricant which shows both internal and external lubricating properties for polyvinylchloride is highly desirable as the overall level of additives in the polyvinylchloride may be reduced through the judicious selection of the proper lubricant. First, the cost of the lubricant system for the polyvinylchloride may be reduced and as the external lubricating agents tend to migrate from the polyvinylchloride it is possible to avoid having substantial quantities of internal lubricant remain in the finished polyvinylchloride article. The polyvinylchloride articles with which the invention is concerned are clear articles such as bottles, opaque sheets, and rigid profiles of polyvinylchloride.
2. Description of the Art
Wilson, in U.S. Pat. No. 3,981,838 issued Sep. 21, 1976 describes various tri-carboxylic compounds which may be esterified and utilized in processing plastics. Wilson states that acid numbers under 2.5 are arbitrarily viewed as essentially tri-esters. Wilson further continues to state that acid numbers greater than that would correspond to a decrease in external lubricity.
Worschech in U.S. Pat. 3,875,069 describes lubricants for thermoplastic materials which are (A) mixed esters of aliphatic polyols, dicarboxylic acids and long chained aliphatic monocarboxylic acids, and (B) esters of the group of dicarboxylic acids and long chained aliphatic monofunctional alcohols; esters of long chained aliphatic monofunctional alcohols and long chained aliphatic monocarboxylic acids; and complete or partial esters of aliphatic polyols and long chained aliphatic monocarboxylic acids in a ratio of (A) to (B) of 1:3 to 9:1. The highest acid number mentioned in the Worschech '069 patent is six with the recommendation that there are no free hydroxyl or acid groups in his lubricant molecule.
In U.S. Pat. No. 4,336,176 issued Jun. 22, 1982, to Lindner, there is disclosed manufacture of polyvinylchloride compounds utilizing an organo-tin compound and a partial ester having functionality as both an internal lubricant and a co-stabilizer for the plastic. U.S. Pat. No. 4,425,458 issued Jan. 10, 1984 to Lindner describes the use of polyguerbet alcohol esters as lubricants for polycarbonate. U.S. Pat. No. 4,487,874 issued Dec. 11, 1984 to Lindner discloses polycarbonate lubricants which were formed from the partial esterification of pentaerythritol.
U.S. Pat. No. 4,690,977 to Hosoi et al, issued on Sep. 1, 1987, describes vinylchloride polymers comprising a grafted polymer, a vinylchloride polymer, a rubber copolymer, and a lubrication system which includes a wax lubricant and epoxidized soybean oil. Hosoi et al makes similar disclosures in U.S. Pat. No. 4,645,795 issued Feb. 24, 1987.
Schofield et al in U.S. Pat. No. 4,797,440 issued Jan. 10, 1989 describes a thermoplastic polymeric organic medium in the presence of a lubricant and a processing additive containing a divalent aliphatic radical. The stabilization of polyvinylchloride is taught in U.S. Pat. No. 4,338,226 issued Jul. 6, 1982 to Worschech et al. The stabilization of the vinylchloride polymers is also taught by Crochemore et al in U.S. Pat. No. 4,102,839 issued Jan. 25, 1978. U.S. Pat. No. 3,951,883 issued Apr. 20, 1976 to Ruchlak et al discloses polyvinylchloride molding compositions.
Tenaka et al in U.S. Pat. No. 4,072,657 issued Feb. 7, 1978 discloses synthetic resins which include vinylchloride-vinylacetate copolymers. U.S. Pat. No. 4,392,581 issued Jul. 12, 1983 to Itsubo et al describes vinylchloride resin compositions. U.S. Pat. No. 3,578,621 issued May 11, 1971 to Stapfer describes stearamide waxes which may be utilized for plastic processing.
This invention deals with lubricant additive systems for polyvinylchloride resins which have superior properties with to metal release and having low gloss.
Throughout the specification and claims, percentages and ratios are by weight, temperatures are in degrees Celsius, and pressures are in KPa gauge unless otherwise indicated. To the extent that any of the references cited herein are applicable, they are hereby specifically incorporated by reference. Ranges and ratios given herein may be combined.